An enduring palaeontological riddle: how many hippopotamid species roamed Sicily? The case study of Amoroso Cave

Hippopotamus pentlandi, although lacking a comprehensive description, is regarded as one of the best known dwarfed hippopotamid species within the Mediterranean region. This study provides a detailed analysis of a hippopotamus mandible from Amoroso Cave (Palermo, Sicily). Morphological and morphometric comparisons with insular and continental species reveal a significant similarity between the Amoroso mandible and some specimens from San Ciro Cave (Palermo, Sicily), as well as with Hippopotamus amphibius. Conversely, material from Cannita Cave (Palermo, Sicily) attributed to H. pentlandi is less robust, more elongated and smaller. 3D geometric morphometric analysis performed on the symphyseal sagittal cross-section further support a closer morphological affinity of the Amoroso mandible to San Ciro Cave specimens and H. amphibius, suggesting an attribution to the latter. Our research reveals the presence of at least two different, potentially coeval, taxa in the Pleistocene of Sicily: the dwarfed Hippopotamus pentlandi primarily known from Cannita Cave, and H. amphibius. While Cannita Cave material has been thoroughly studied over the years, abundant remains from other localities, e.g. San Ciro Cave, require re-evaluation. A thorough analysis of Sicilian hippopotamids is crucial to improve our understanding of their systematics and to provide new insights into the palaeobiogeography, palaeobiology, and palaeoenvironment of Sicily during the Pleistocene.